388 PART IV. CLASSIFICATION. 



first root eventually springs adventitiously from cells belonging to the 

 upper tier, below the cotyledon : its origin is exogenous. (Compare em- 

 bryogeny of Selaginella, p. 393). 



Vegetative Propagation. In the creeping forms, as the main stems die off, 

 the younger branches become independent and constitute new individuals. 

 In some species there are gemmae, as in L. Selago, where they are borne on 

 the stem, and are modified leafy branches ; and as in L. cernuum, where 

 they are small tubercles borne on the roots. 



THE GAMETOPHYTK. In so far as the gametophyte has been investigated, 

 it is a monoecious prothallium, either containing chlorophyll (L. inun- 

 datum and cernuum), or destitute of chlorophyll (L. annotinum and Phleg- 

 maria) and saprophytic. 



The morphology of the prothallium offers considerable variety. In 

 some species (e.g. L. inundatum) the prothallium is tuberous ; its base is 

 embedded in the soil, and bears root-hairs ; its apex projects above the 

 surface and bears a tuft of green leafy lobes : the sexual organs are de- 

 veloped in a zone from a layer of tissue which long remains merismatic 

 and which is situated just below the apical tuft of lobes ; occasionally 

 some antheridia are developed on the lobes. Whilst in these species the 

 prothallium is very small and simple, in L. PJilegmaria and some other 

 species it is considerably larger and more complex. It consists here of 

 a cylindrical, monopodially-branched body, with apical growing-points 

 similar in structure to those of the sporophyte. The superficial layer of 

 cells, representing an epidermis, gives rise to a number of root-hairs. 

 The sexual organs are developed on special branches, yametophores, though 

 antheridia sometimes occur on the vegetative branches ; the gametophores 

 are shorter and thicker than the vegetative branches, sometimes even 

 tuberous, and on the upper surface bear the sexual organs surrounded by 

 stout multicellular hairs, paraphyses. 



The male organs (antheridia) are sunk in the tissue of the prothallium : 

 they resemble those of the Eusporangiate Filicirise. Their development 

 precedes that of the female organs. 



The male cells are spermatozoids, oval in shape, and have two cilia. 



The female organs (archegoma) have short necks which project but 

 little above the surface of the prothallium ; they have the structure 

 usual among Pteridophyta. 



The female cell (oosphere) requires no special description. 



In consequence of its position and of its mode of development, the 

 embryo is forced downwards into the tissue of the fleshy prothallium, being 

 anchored, as it were, at one end by the suspensor (see p. 347). As it grows 

 it destroys the cells of the prothallium with which it comes into contact, 

 and absorbs the nutritive substances stored in these cells by means of the 

 so-called foot, the superficial cells of which grow out into short papillae. 

 In its further growth the embryo becomes more and more curved until it 

 regains the surface of the prothallium and projects. In L. Phleymaria 

 the embryo remains for some time enclosed in a sac, the calyptra, formed 

 by active growth of the prothallial tissue. 



The life of the prothallium is short and closes, in most cases, with the 



